Demonstrators hold up signs at the entrance of Bonelli Park for President Barack Obama's visit, where he will designate a portion of the San Gabriel Mountains as a national monument in San Dimas, Ca., October 10, 2014. (Photo by John Valenzuela/Inland Valley Daily Bulletin)

A group of protesters gathered outside Bonelli Park Friday morning in advance of President Barack Obama’s visit there later today. (Photo by Watchara Phomicinda/San Gabriel Valley Tribune)

President Obama will designate the mountains the nation’s newest national monument at an event starting at 1 p.m.

The newest monument is a 346,000-acre stretch of land from Castaic to the Los Angeles/San Bernardino County border and is part of the Angeles National Forest — a playground for 19 million Southern California residents.

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